The production of substrates comprising cellulosic fibers and a thermosetting resin composition useful, for example, in supporting decorative layers in the formation of high pressure decorative thermoset plastics laminates is well known. Conventionally, said substrates comprise a plurality, i.e. about 2-10, of paper core sheets impregnated with a liquid thermosetting resin composition, said core sheets being prepared by impregnating a web of paper, prepared by a wet-laying process, with a solution or dispersion of a thermosetting resin composition in a volatile solvent, drying said impregnated web to reduce the volatile matter content to a desired level and cutting said impregnated, dried paper web into sheets of the required dimensions. Sufficient core sheets are normally employed to provide laminates having thicknesses of about 0.25 mm-2.25 mm.
Recently, it has been found that high pressure consolidated articles such as decorative laminates produced from a thermosetting resin containing fibrous cellulosic substrate, wherein the disadvantages of such articles made by conventional sheet processes are overcome or diminished, may be produced by using, as the substrate, an air-laid web comprising both cellulosic fibers and a thermosetting resin. These high pressure articles exhibit a toughness superior to those produced conventionally which contain, as their core, a plurality of thermosetting resin impregnated Kraft paper sheets. This toughness is evidenced by the articles' increased resistance to stress-cracking. Additionally, these pressure articles also exhibit substantially equivalent uniform strength and dimensional properties regardless of the machine direction from which the measurement is taken.
One of the most difficult to solve problems the consolidated article industry has been faced with in recent years is to improve the flame-retardancy of the articles so that they can be used in particular service applications wherein non-flammability is critical such as on ships and naval vessels.
When producing such articles from core materials composed of a plurality of resin impregnated paper sheets, the addition of flame-retardant additives must be accomplished either during the production of the paper sheets per se or during the impregnation of the sheets with resin. To retain the flame-retardant additive in the paper during the paper-making process is extremely difficult and to add the additive during paper sheet impregnation with the resin requires that either the resin be a solvent for the flame-retardant or that the resin bath be continuously agitated to retain the flame-retardant in suspension in the resin bath while the paper is passing therethrough.